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Cmfb Simulation

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58 Threads found on Cmfb Simulation
Hi All, I'm still on TT polyphase filter with current input and I saw a strange behavior in this structure when I'd simulated the CP1. My Opamp is a classical 2 stages with a cmfb on activ load. In Open loop the gain is 58dB for a UGF at 27MHz and Phase margin is 45 degree. The stange behavior is the following: In the global strucure, when
... second question was : what is the real gain of main amp? with cmfb or without it? With cmfb of course, as both circuits have to cooperate in reality (in practice). do we have to put the main or cmfb in unity-gain config? Of course not,
Additionally, if you do a time domain simulation and apply a common mode step up down to the input of your amplifier, you can monitor to see if your stable if no ringing occurs. Additionally, it might be interesting to see how well your cmfb regulates to your common mode level, AKA offset. JGK
Hi,everyone I've got some questions about cmfb stability in two-stage op amplifier. 1) Figure 1 is a schematic of two-stage opa with continuous cmfb circuit. I insert a device of iprobe (in analogLib library) to simulate the loop gain and phase of cmfb circuit. Figure 2 shows a voltage buffer using the two-stage opa. As we (...)
hello friends I have designed the folded cascode opamp...(fully-differential)....i have added SC-cmfb circuit to Amplifier ....but i am getting problem in simulating with PSS and PAC analysis.. my detailed steps for the analysis are as follows... set pss simulation for clock of 2.56MHz and input signal of 256K
when I do cm stb simulation in three_stage OP,I add L=500p to power and ground. the result shows that a peak in f=9.6G. If I delete L in power and ground,there in no peak in cm stb result. Why? please help me. thanks!
i have designed a two stage fully differential opamp with hybrid ahuja compensation (that is, two compensation capacitor used in the two cascode nodes of each branch), the first stage is folded cascode, the second is common source, and the cmfb is continuous common mode feedback which have two input pairs, one pair connected to vcm, the other pair
Hi, all Somebody in this forum said that, the OTA with S/C cmfb simulation could be done by PSS, PAC...., with spectreRF, but could anyone explain the detailed procedue or just give me some documents on that? I need it badly now! thanks a lot, and best regards Added after 5 hours 17 minutes: I tried t
Yes you can still use loopgain simulation methodology in cadence. However before running "stb" analysis you have to run transients till your CM is settled. An easier way is to use ideal cmfb circuit and then do can skip the transient analysis part. My answer assumes you already have good background simulation experience in spectre. Let me (...)
the output voltage is digital signal how could I do ? the cmfb circuit is designed with sc circuits I'm afraid that ac analysis couldn't carry out I perform pss and pac ,however the circuits doesn't converge when pss simulation general idea for psrr simulation can be : put a ac source in supply vsupply
I have same problem. I have designed amplifier which in AC simulation with ideal cmfb (using system from several VCVS) achieves about 75dB gain. Using PSS and PAC with real SC cmfb I achieve about 33dB. It is strange that in spectre.out file for DC levels for OUTP and OUTN are about 300mV output N cascodes are in triode region, but if I plot (...)
Hello, I have designed a fully differential folded cascode OTA with SC-cmfb. I haver tested the circuit using a SC-cmfb network using Verilog-A macromodel switches. And the OTA seems to work very well. When I replace the switches with transistors the clock injection is so bad that the cmfb voltage never is mantained at a fixed value (...)
hi, i'm confused by a problem like this: i design a fully 2-stage opamp with continue cmfb. and the ac analysis show dc gain is 90db ,also have go0d phase response. but after post-simulation ,the gain is only 50db! and To make things worse, the phase have Obvious Curved-up before the gain to 0db ! my opamp layout is almostly Symmetrical. and have
HI, anybody has some good ideas to simulate the AC characteristics of the differential opamp with switched capacitor cmfb circuit? Because the switched capacitor has no DC operating point, so how to deal with it in AC analysis? thanks.
Hi I`m desing a rail to rail folded cascode Op amp I have some question in Fully diff Amp 1: How to modeling the ideal SC cmfb Now I using the resistor and capacitor cmfb 2: How to simulation the Fully diff amp ICMR , SR Textbook(allen) describe thd single ended amp
I think cmfb is definitely needed for simulation like differential or common mode. One way to split differential and common mode is to use balun. For simplicity, you can implement an ideal cmfb like VCVS to simulatate differential behaviors. Please refer the following link for VCVS. Happy 2009
Can anyone tell me the procedure or show me the link/tutorial......etc about SC-cmfb simulation? How to simulate common mode Loop gain and phase margin of the ota with SC-cmfb? thanks in advance.
Dear all~! Thanks in advance! I simulate differential input, output amplifier without cmfb. Because output impedance is high and there is not cmfb, output dc voltage goes near VDD. And, the AC simulation result is wrong. How do you simulate Fully differential Amplifier? Please let me know how I set the test bench. (...)
Does anybody know how to do the AC simulation for fully-differential OTA with sc-cmfb? This is what I have heard: 1) use vcvs to model the sc-cmfb; however, what should I put the gain for the vcvs? A very large value? Please look at the attachment for the schematic. 2) Use the pac (in spectre) Thanks a lot.
Hi friends, I am starting to design a folded-cascode fully differential amplifier OTA with cmfb. I am confused and don't know how to start because of the large number of mosfets. I know that the ideal flow is to start with hand analysis then move to the simulation stage, but I have two problems with hand-analysis, first is the
No! in simulation, the circuit maybe operate. But you must use cmfb for fully differential amplifier. Or you can use it without cmfb in case of single ended gain booster.
i want to simulate the op's gain ,GBW,etc, but the op's cmfb is sc cmfb, and the op's loads is the next sc integrator. how to caculate the op's loads and how to substitude the sc cmfb circuits in simulation circuits? thanks!
hi, i design a telescopic cascode OPAMP with SC-cmfb, but .tran simulation result shows that there is offset about 20mv between output voltage and Vcmo(1.65v). the curve is not flat . what's the problem with this?thanks! and how to simulate the settling time of one full differential OPAMP with SC-cmfb?when i simulate it in closed loop (...)
Typical gain for such circuit is more 100dB (process > 0.5um). So at the first you need to check that each MOSTs operate in saturation. Also check cmfb circuit. I hope u don't forget include cmfb in simulation.
iam designing a fully differential folded cascode OTA gain: 66 db Vdd: 3.3 V power dissipation 3.7 mW BW: 980 Mhz I have used switched capacitor cmfb(Common Mode Feed Back) Problem: Iam getting gain of 54 dB and power dissipation of 2.7mW but the problem is that the gain curve is not crossing 0dB it reaches a minimum value of 1db at a fre
I have search the similar topic in EDAboard but I just get the way to simulate it in Hspice. But in my lab we use cadence as simulation tools so I want to know the way which can be used in Cadence. 3x!
If I use sc cmfb, is AC simulation still work? It not continous and how can I get the gain of Opamp now? u can use PSS & PAC to get the AC simulation result~
which kind of cmfb do you use? SC or continuous
Hi~ all~~ I desinged fully differential op amp. The structure of op amp is two stage amp with cmfb circuit. The specification is like that : Gain is more than 60dB, unit gain bandwidth is more than 100MHz and phase margin is more than 85degree. The simulation result is like that : loop gain is 57dB(@40MHz
ideally, the cmfb gain should be infinite to ensure the output level to be equal the reference voltage. as to the simulation of the cmfb, you can first break the cmfb loop at cmfb output point, and apply a voltage source with 1V ac magnitude in to the opamp at the break point , make sure that ac (...)
I design a fully differential opm with cmfb. when the offset is good, the linearity is bad; when the linearity is good, the offset is bad. How can statisfy both linearity and offset. Please thanks
I got a small doubt while simulaiton in hspice .Like we use cmfb in Op-amps so that the circuit functions well even if there is any mismatches in the current mirrors.Say i use level 49 model file and simulate it ,will such things be incorporated during simulation .I mean suppose i do not get an o/p for an opamp without cmfb in (...)
for example, in Hspice following description "ecmfb vcmfb vss poly(4) vb1 0 vcmref 0 vop 0 von 0 0 1 -1 0.5 0.5" is function as a idesl cmfb block Similarly, Can I use the ideal cmfb block in Spectre simulation? What's the name of that block
how to simulation the AC of amplifier with Switch-capacitor cmfb? thanks in advance!
in the picture,when phase 1 come, Vcm and Vbn create a voltage difference on the capacitor,when phase 2 come,the voltage difference is feedbacked to the lower transistor pair,and phase1 and phase 2 do not overlap but the simulation gives this result, periodic output dc level and some ripp
How to simulate the stability of SC cmfb loop in a full differential OPAMP?
If the common mode feedback (cmfb) circuit is made of switched capacitor (SC) circuits, this is a significant diference from single end amplifier.
i am a newbie in analog design , but i have a question about ur OTA used in cmfb i dont get what u r doing as the bias of the OTA is done by two current sources, which means "to me i guess" that u need a cmfb for that OTA also , i think u should use something like diffrential to single ended OTA "unbalanced". Added after 3
Hi~~ when we design a SC-cmfb based opa often use PSS & PAC to analysis it gain & phase Margin. But when i take off the cmfb the phase Margin is smaller . My question is : when we use SC-cmfb the simulation is only care PAC & PSS , can neglect ac analysis ? thanks~~~!!!
Dear : Please see these topics. Best Regards, mpig
hello, i was checking the stability of a cmfb loop , so i tried using the stability analysis in Cadence i got the PM and GM, but i want to know the zero's and pole's for compansation, my question is can i cut the loop in any node "and add AC source wth approximate DC of this point taken 4m transient analysis", or there is some kind of better nod
build an ideal cmfb with vcvs, cap etc. do not use switch you can gain the same function
I designed a folded fully differential amp with sc cmfb used in pipeline. When the clock freq is low, like 1M, this amp can get a Av about 10K. But when the freq is up to 40M, the Av is only 400. I did this simulation in spectrel using pss and pac ananlysis. Is it a problem of sc cmfb or the amp itself? I try to reduce the capacitance (...)
Dear all: I designed an AMP with switch-capacitor cmfb. but i don't know how to simulate the open loop gain and GBW of this AMP. When i do this simulation,i replaced the sc cmfb with an ideal cmfb in the AMP,then i can get these results,but i don't know whether these results are the same as SC cmfb. (...)
hello, guys, I have designed a diff amp with SC-cmfb, the phase margin need to be opitimized, when i do ac simulation, the SC-cmfb should be took out, so my question is whether the capacitor in SC-cmfb be one part of Cload?? thanks a lot. B&R Yes, because SC-cmfb introduce some loading effect to your (...)
I was requested in my class to design a high-swing Telescopic-cascode fully-differential OTA to work in a voltage buffer (shown below) in an ADC. The expected load is shown below. There is additional loading of 1 pF at each of the OTA output nodes (not shown). The amplifier is required to accommodate a maximum swing of
Hi, I think u should be able to have your amp bias point set without the cmfb. One of the purpose of the cmfb is to counter the mismatch effect in real circuit and keep the bias point constant. In simulation, you do not encounter this effect. If you set the size of transistors and DC voltage in the 2 branches to be the same you will have (...)
Howdy- I'm currently designing an OTA for sigma-delta modulators. When continuous-time cmfb is utilized, all the simulations show good results. However, when I change to switched-cap cmfb, trans simulations are okay, but how to simulation the AC response? Any hints?
Many books say thermal noise in two-stage Opamp is dominated by that in first-stage. Because that in sedond-stage is divided by first-stage gain and second-stage gain. And I did noise calcalation of Two-stage Opamp with cmfb by using simulator and hand-calculation. But these results have big differences in value. But I'm not able to under
Hello Everybody, I attach a figure below which shows fully-differential fold-cascode one stage opamp with SC-cmfb. Then in my next post, there is another figure, which I think it can be used as cmfb structure with equavilent resistors (which I call R-cmfb here). This cmfb structure is variant from Razavi book on page (...)